1. Field of Invention
This invention relates to the reamer cutting head for the surgical reamers used by surgeons during intramedullary reaming and other orthopedic procedures requiring the internal enlargement of bone central canals.
2. Brief Description of the Prior Art
Surgeons have for years used reamers during orthopedic surgery to enlarge intramedullary canals of long bones such as the femur, tibia and humerus. The purpose of this is for sizing or enlarging the canal for the acceptance for an intramedullary fixation device or total joint implant. This fixation device is usually a rod or tube inserted into the correctly sized canal and held in place with screws.
Intramedullary reaming is generally performed with a rotary cutting tool attached to a flexible shaft. Reamer cutting tools are mounted permanently to a flexible shaft or are interchangeable by means of an interlocking dove tail slot.
Prior to the reaming process a wire rod is inserted into the central canal as a guide for the reamer. The reamer and shaft each have an axial bore concentric with the axis of rotation. The reamer is passed over the rod and feed into the canal for enlarging. The canal is enlarged incrementally with a series of reamers, which increase in diameter by 0.5 mm. A separate interchangeable cutter head or complete cutter head/shaft assembly is required for each step. This requires that the reamer be extracted from the canal and slid off the guide wire. The next incremental cutter head or complete cutter head/shaft assembly is then passed over the wire and advanced into the canal. For an intramedullary nail this would entail approximately 9 or 10 interchanges.
The prior art cutting heads have been cylindrical, elliptical, ball or bullet shaped with a plurality of fluted spaced around the axis of rotation. Each flute has a cutting edge formed when a "V" groove is machined along its axis from the front tip to the rear end of the cutter. Generally, straight or helical "V" grooves are machined into the cutter in order to create a rake angle at the leading edge.
This "V" groove also serves as an area for chips and tissue after being cut from the internal surface of the bone canal. Such a cutter head is shown generally in U.S. Pat. No. 4,706,659 (Matthews et. al.) and U.S. Pat. No 4,751,922 (DiPietrolo) as a cutting head on a shaft but does not refer to the design of the cutting head. Borzone et. al. (U.S. Pat. No. 5,122,134) describe a cutting head having a series of circumferentially spaced flutes having a first section extending in a straight line from the leading edge of the cutter, a curved central portion formed as a section of a torus, and a second straight section back to the trailing edge of the cutting head.
The form of the "V" groove machined into the cutter creates the rake angle and cutting edge of the first flute and the trailing edge of the next adjacent flute. By varying this "V" angle and depth with respect to the number of flutes required, a constant circumferential width along the cutting surface is formed. This constant circumferential width generally starts at the front tip and extends to the rear end of the cutter. Each of the flutes has a cutting edge and when rotated, forms the cutting surface of the reamer. This cutting surface has a ground relief angle to enable it to cut freely.
The prior art reamer heads have been concerned with cutter binding in the bone canal and cutter retraction after binding. The general configuration of prior art reamer heads have not addressed the problems of heat generation, cutter force, intramedullary pressure and the quantity of cutter heads required to enlarge the intramedullary canal.